A novel reaction for annulation onto α,β-unsaturated ketones:: W(CO)5•L promoted exo- and endo-selective cyclizations of ω-acetylenic silyl enol ethers prepared by 1,4-addition of propargyl malonate to enones

[GRAPHICS] A highly useful method for five- and six-membered ring annulation onto alpha (1)ss -unsaturated ketones is described. 1,4-Addition of propargylmalonate to alpha ss -unsaturated ketones in the presence of silyl triflate gives 7-siloxy-6-en-1-yne derivatives in good yield. W(CO)(5).L-catalyzed cyclization of these substrates can be induced to give preferentially either exo- or endo-cyclized products in good yield simply by changing the reaction solvent.